Modified porous starch

ABSTRACT

The present invention relates to microporous starch granules surface coated with a hydrophobic agent said granules useful in absorbing hydrophobic malodorous materials either from the liquid or gas phase. The hydrophobic granules are useful in controlling the malodors associated with catmenials and hygienic undergarments as well as being useful for absorbing unwanted food and other environmental malodors.

CROSS REFERENCE

This application claims priority under Title 35, United States Code119(e) from Provisional Application Ser. No. 60/025,933, filed Sep. 11,1996.

FIELD OF THE INVENTION

The present invention relates to a surface coated modified starch matrixuseful for absorption of malodor. The present invention also relates tomethods for absorbing hydrophobic materials from the air or aqueousmatrices.

BACKGROUND OF THE INVENTION

The suppression or elimination of odors, particularly undesirable odors,has been the objective of countless investigations. Malodors have theirgenesis in many forms but those that are of most consequence to humanbeings are those involving occasional or repeated daily exposure. Ofprimary concern are those malodors that are caused by normal bodilyfunctions, for example, the urine and feces odors associated withinfants and the malodors associated with menses.

Cultural and aesthetic standards have influenced the permissible levelof human and environmental malodors and control of these odors has beenthe focus of investigation for many centuries. In general, theseinvestigations have been focused on either of two approaches, namely:(a) odor masking, in which a substance of strong yet relatively pleasantodor is introduced into the proximity of a less pleasant odor sourcewith the intent of overburdening the olfactory receptors with thedominant pleasant odor, or (b) sequestering the undesired odoroussubstance in a non-volatile form either by chemical reaction, adsorptionor absorption on a sorbent material exhibiting a preference for theodorous substance.

Odor masking, although effective in the short term, has certainlimitations. First, masking does not remove or eliminate the source ofthe malodor. Secondly, when scents and perfumes are used to overcomemalodors, the user must make sure an effective and constant level ofmasking agent is present to avoid too low a level of masking agent thatmay not be sufficient to cover-up the malodor. In turn, too high a levelof masking agent may itself produce an undesirable effect. The prematuredepletion of the masking agent can be an additional concern.

Sequestration has thus become the method of choice for elimination andcontrol of both human and environmental malodors. The more effectiveapproach has been to sequester the undesired malodor primarily byadsorption.

By far the most commonly employed of the solid adsorbents are activatedcharcoal or active carbon, although silica gel, activated alumina,kieselguhr, Fullers earth and other clay minerals and zeolites, alone orin combination, have also been proposed as odor "adsorbents". In U.S.Pat. No. 4,437,429, to Goldstein et al., issued Mar. 20, 1984, the useof a hydrated zeolite in admixture with clay is proposed as beingparticularly useful for the control of odors from pet litter. Though itis observed that the use of zeolites by themselves as litter materialhas generally been unsuccessful due to their poor water adsorptionproperties as compared with clays. However, these absorbents are directto methods of soaking up moisture or liquids whereas, described hereinbelow, the present invention is directed to the absorption of volatilesubstances without the necessity to absorb any liquid carrier material.

The use by women during menstruation of sanitary napkins, pads, andpanty liners has become common place. Although natural fluids producedduring menstruation are suitably absorbed by the catamenial absorbentmaterial thereby protecting clothing from damage, the problem of malodorpersists. This is due in part to the fact that many chemical compoundsresponsible for malodor typically have very low odor detectionthresholds and are perceptible at the part per million (ppm) level. Inaddition, may of these malodorous materials are hydrophobic easilypartitioning out of the liquid phase as the fluids are absorbed by thecatmenial substrate material.

It has now been surprisingly found that modified starch granules can becoated with surface modifying agents producing microporous hydrophobicgranules that readily absorb malodorous agents even when the agents arein the "gaseous" state. For example, when menstrual fluid is absorbedonto a substrate, volatile low molecular weight compounds neverthelesscan still escape into the gas phase resulting in the release ofmalodors. The modified starch granules of the present invention containmodified surfaces that absorb these and like malodors therefore removingthem from the air.

Modification of porous starch granules by partial solubilisation withalpha-amylase for use as dusting powders and talc is described inEuropean Patent Application 182,296, published May 28, 1986. However,the purpose of the modified starch granules is the complete absorptionof moisture without concomitant caking.

Other modified starch materials have been described, for example, U.S.Pat. No. 4,985,082 to Whistler, issued Jan. 15, 1991, which disclosestreated granular starches derivatized to enhance the absorptiveproperties. This patent discloses the specific use of interiorcrosslinking agents to strengthen the granules against collapse when toomuch moisture is absorbed. This patent relates to releasable containmentof an absorbate whereas the present invention preferably does notrelease the volatile materials once absorbed.

BACKGROUND ART

Further publications related to porous modified substrates or starchhydrolysates are U.S. Pat. No. 5,445,678, Whistler, issued Aug. 29,1995; Japanese Patent Applications 01157903 A and 01218882 A.

SUMMARY OF THE INVENTION

The present invention relates to an absorbent starch material suitablefor absorbing volatile compounds having a hydrophobic affinity,comprising:

a) a partially hydrolyzed porous starch matrix; and

b) a siloxane surface modifying agent applied to the porous starchmatrix.

It is a further object of the present invention to provide a method forremoving volatile malodor compounds from a liquid comprising the step ofcontacting the fluid containing malodorous volatile compounds with theabsorbent material of the present invention.

All percentages, ratios and proportions herein are by weight, unlessotherwise specified. All temperatures are in degrees Celsius (° C.)unless otherwise specified. All documents cited are in relevant part,incorporated herein by reference.

DETAILED DESCRIPTION OF THE INVENTION

Partially Hydrolyzed Porous Starch Matrices

The absorbent starch materials of the present invention comprise anenzyme modified starch granule treated with a surface modifying siloxanepolymer. The starch granule is modified in that treatment of the granuleaffords a pore void volume of about 10% to about 65%, preferably fromabout 10% to about 50% more preferably from about 20% to about 40% thevolume of the granule. Applied to this modified starch granule is asurface modifying siloxane polymer in an amount from about 0.01% toabout 10%, preferably from about 0.1% to about 1%, more preferably fromabout 0.5% to about 0.75%, by weight of the starch. This enzyme modifiedstarch granule constitutes the "hydrolyzed porous starch matrix" of thepresent invention.

The terms "porous starch" and "microporous starch" are usedinterchangeably throughout the description of the present invention andare taken to mean "starch or starch granules having been modified by asubstrate, preferably and enzyme, resulting in the structural lattice ofthe granule having holes, pores or openings which allow smallermolecules to enter the interstices of the starch granules".

The starch granules suitable for modification and for use in the presentinvention may comprise any starch which is capable of modification toincrease pore volume or surface area, for example, corn or potatostarch, having a preferred particle size of from 10 to 50 micron.However, this invention is not limited the aforementioned particle sizerange. The source of starch granules for use in the present invention isdiscretionary to the formulator.

An example of porous starch granules suitable for use in the presentinvention are starch granules modified by treatment, usually by amylaseenzymes, to increase the void volume and thereby producing a microporousstarch matrix. Any of a wide variety of art-recognized alpha-amylase orglucoamylases including those derived from Rhizopus niveus, Asperigillusniger, and Rhizopus oryzae and Bacillus subtilis and alpha-amylases andglucoamylases of animal origin, can be used. Alpha-amylases having afungal origin are especially suitable for use in the present invention.Preferred amyloglucosidases are Rhizopus sp. (Sigma A 7255) andAsperigillus niger (Sigma A 3042). A preferred alpha amylase is thatderived from Asperigillus oryzae (Sigma A 0273). Bacterialalpha-amylases are also suitable for use in the present invention, forexample, Sigma A 6380, NOVO LE17, NOVO SP722, NOVO SP690, including thealpha amylase derived from genetically engineered variants of Bacillussp. such as NOVO SE22. Also suitable is the porcine pancreas amylase,Sigma A 4268. Most preferred are the fungal amylglucosidase fromAsperigillus niger available from NOVO as AMG 300L.

Microporous starch granules prepared by the action of acid or amylase ongranular starch are well known in the literature, see for example,Starch Chemistry and Technology, Whistler, Roy L., 2nd Edition, (1984),Academic Press, Inc. New York, N.Y. These methods and others, as well asthose disclosed herein, are suitable for preparing a partiallyhydrolyzed porous starch matrix.

The duration of enzyme treatment necessary to produce microporous starchmatrices suitable for use in accordance with this invention depends on anumber of variables, including the source of starch, species andconcentration of amylases, treatment temperature, and pH of the starchslurry. The progress of starch hydrolysis can be followed by monitoringthe D-glucose content of the reaction slurry. In a preferred embodiment,the starch hydrolysis reaction is allowed to proceed until about 17 toabout 20% of the starch has been solublized.

Siloxane Surface Modifying Agent

The silicone polymers useful for the present invention are thosesiloxanes that can be used to suitably coat the surface of the modifiedstarch granules rendering the surface of the starch granuleshydrophobic. In general, silicone denotes a synthetic polymer having theformula

    [R.sub.n SiO(.sub. 4-n)/2].sub.m

wherein n has the value from 1 to 3 and m is greater than or equal to 2.These materials contain a repeating silicon-oxygen backbone and haveorganic groups R attached to a significant proportion of the siliconatoms by silicon-carbon bonds. The terms "silicone" and "siloxane" areused interchangeably throughout the description of the present inventionand are taken to mean the silicon containing polymers used to modify thesurface of the starch granules. Further descriptions of silicones can befound in the literature, for example, Kirk-Othrner Encyclopedia ofChemical Technology, 3rd Ed. vol. 20, p. 922.

Preferred siloxane polymers suitable for use as a hydrophobic coatingaccording to the present invention have the formula ##STR1## wherein R¹units are hydrocarbyl units, preferably C₂ -C₂₂ linear alkyl, C₃ -C₂₂linear alkenyl, C₂ -C₂₂ branched alkyl, C₃ -C₂₂ branched alkenyl,phenyl, benzyl, phenoxy, benzyloxy; R² units are --(OR³)_(n) R⁴ or--(CH₂)_(m) (OR³)_(n) R⁴ wherein R³ is C₂ -C₁₂ alkylene; R⁴ is hydrogen,C₂ -C₁₂ alkyl, --NR⁵ R⁶ wherein R⁵ and R⁶ are each independently C₂ -C₂₂linear alkyl, C₃ -C₂₂ linear alkenyl, C₂ -C₂₂ branched alkyl, C₃ -C₂₂branched alkenyl, phenyl, benzyl, phenoxy, benzyloxy, and mixturesthereof R⁴ units are preferably hydrogen or methyl. The value of m isfrom 1 to 22; the value of n is from 1 to 22; the value of x is from 0to about 10,000; the value of y is from about 0 to about 10,000; thevalue of z is from 0 to about 10,000.

R² units comprising --(OR³)_(n) R⁴ units can be formed from one or moredifferent R³ units. For example, --(OR³)_(n) R⁴ may be rewritten as--(OR^(3'))_(n') (OR^(3"))_(n") R⁴ wherein n'+n"=n, for R² units havingtwo types of alkyleneoxy units. In a like manner --(OR³)_(n) R⁴ may berewritten as (OR^(3'))_(n') (OR^(3"))_(n") (OR^(3'"))_(n'") R⁴ whereinn'+n"+n'"=n when three different alkyleneoxy units comprise R². Anexample of --(OR³)_(n) R⁴ equal to --(OR^(3'))_(n') (OR^(3"))_(n") R⁴comprising both ethyleneoxy and propyleneoxy units has the formula##STR2## wherein n'+n"=n=8, R^(3') is ethyleneoxy, R^(3") ispropyleneoxy and R⁴ is methyl.

Examples of preferred siloxanes suitable for use in the presentinvention are the siloxanes available from Goldschmidt ChemicalCorporation sold under the tradename ABIL®, for example, ABIL® AV20-1000, ABIL® B 9800, ABIL®D B 9801, ABIL® WS 08, ABIL® WE 09.

The siloxane surface modifying agents are readily applied to the surfaceof the modified starch by contacting a sample of water-free starch withthe siloxane dissolved in a suitable non-polar solvent such as toluene,xylene, hexane, and isopentane. However, this list of solvents is notmeant to be inclusive of all solvents suitable for use in the practiceof the present invention. The formulator may also employ mixtures ofsolvents.

Contacting surface modified porous starch granules of the presentinvention with an aqueous medium containing malodorous hydrophobiccompounds will have the effect of removing the malodorous compounds fromthe aqueous medium with a minimal absorption of water. When used assuch, the porous granules of the present invention are considered to beselectively extracting malodorous hydrophobic materials. Because thestarch granules of the present invention are modified to have a highlyhydrophobic surface area, the malodorous compounds have a higheraffinity for the porous starch granules than for the surroundingaqueous-based media.

It is a typical practice for grocery stores, butcher shops and otherretail handlers of fresh meat, poultry and fish to package the meat,poultry or fish product in a package or wrapper having a blood or otherfluid absorbing article. Impregnating this absorbing article with themodified microporous starch granules of the present invention is anotherexample of using the modified microporous starch granules to mediate theformation of malodorous materials within the present invention.

The present invention also consists of a method for absorbing amalodorous hydrophobic compound from an aqueous-based medium comprisingthe step of contacting the aqueous-based medium with a surface modifiedstarch granule comprising a partially hydrolyzed porous starch matrixand a siloxane surface modifying agent applied to the porous starchmatrix.

The term "aqueous-based medium" is defined as a fluid material the majorliquid component of which is water. Examples of an aqueous-based mediumare blood, urine, and feces. However, an aqueous-based medium can alsocomprise water that has been used to solublize a solid or to extract asolid material. For example, an aqueous-based medium once dried of allfluid including those volatile liquids other than water may bereconstituted with water to re-form the aqueous-medium.

The surface modified microporous starch granules of the presentinvention can also be applied to fabric, for example draperies,curtains, outerwear, etc. to absorb malodors that come into contact withthe fabric. For example, cigarette smoke in a room may be suitablyabsorbed when the granules of the present invention are applied to thecarpeting and other fabric (upholstery) within a room. Simple vacuumingof the granules removes the used particles containing the entrainedmalodors and then a fresh supply of granules can be applied at theconvenience of the user.

The present invention also comprises a method for absorbing ahydrophobic material comprising the step of contacting the hydrophobicmaterial having a ClogP greater than 1 with a surface modified absorbentcomprising a partially hydrolyzed porous starch matrix and a siloxanesurface modifying agent applied to the porous starch matrix.

The hydrophobic material which is removed may be a material that is notmalodorous but is nevertheless undesirable for other aesthetic reasons.These hydrophobic materials typically have a ClogP greater than 1. Thehydrophobic material having a ClogP greater than 1 may be a freelydispersed material in the air or the material may be dispersed in anaqueous-based medium.

The hydrophobic materials removable or irreversibly absorbable by themodified microporous surface coated starch granules of the presentinvention are characterized by the calculated logarithm of theiroctanol/water partition coefficient, ClogP. The octanol/water partitioncoefficient of a hydrophobic species is the ratio between itsequilibrium concentration in octanol and in water. Since the partitioncoefficients are frequently large, they are more conveniently given inthe form of their logarithm to the base 10, logP.

The logP of many hydrophobic species has been reported; for example, thePonmona92 database, available from Daylight Chemical InformationSystems, Inc. (Daylight CIS), contains many, along with citations to theoriginal literature.

However, the logP values are most conveniently calculated by the "CLOGP"program, also available from Daylight CIS. This program also listsexperimental logP values when they are available in the Pomona92database. The "calculated logP" (ClogP) is determined by the fragmentapproach of Hansch and Leo (cf., A.

Leo, in Comprehensive Medicinal Chemistry, Vol. 4, C. Hansch, P. G.Sammens, J. B. Taylor and C. A. Ransden, Eds., p. 295, Pergamon Press,1990, incorporated herein by reference). The fragment approach is basedon the chemical structure of each hydrophobic compound, and takes intoaccount the numbers and types of atoms, the atom connectivity, andchemical bonding. ClogP values are the most reliable and widely usedestimates for octanol water partitioning. It will be understood by thoseskilled in the art that experimental log P values could also be used.Experimental log P values represent a less preferred embodiment of theinvention. Where experimental log P values are used, the one hour log Pvalues are preferred.

For example, the surface modified microporous starch granules of thepresent invention may be placed in the path of free flowing air whichcontains malodorous compounds or compounds that have a ClogP valuegreater than 1, preferably greater than 2, more preferably greater than3, most preferably greater than 4. The surface modified starch granulesof the present invention, because of the high pore volume andirreversible nature of the hydrophobic absorption, can be used to absorbunwanted odor that form on a continuing basis, for example, the starchgranules can be placed in a refrigerator where the commingling of foodaromas or malodors odors is undesirable.

The materials of the present invention absorb hydrophobic compoundswhich are typically responsible for malodor from liquid or aqueous-basedmedia. The presence of a hydrophobic liquid or other aqueous based fluiddoes not diminish or prohibit the absorption of these malodorouscompounds.

The relative hydrophobicity of the modified starch granules can bemeasured using one or more techniques common to the art. For example,modified corn starch and modified corn starch coated with a siloxanepolymer are heated in an oven. The samples are removed and placed in aconstant humidity environment and are allowed to re-absorb water fromthe atmosphere. The difference in the amount of re-absorbed waterbetween the two samples can readily serve as a basis for expressingrelative hydrophobicity. The formulator may also correlate thisdifference in water re-absorption with the amount of siloxane thateffectively coats the modified porous starch granules thereby adjustingthe amount of siloxane polymer to fit the desired hydrophobicity.

The following non-limiting examples illustrate the preparation and useof the siloxane coated modified starch granules of the present inventionfor control of malodor.

EXAMPLE 1

A 22 L round-bottom flask is charged with acetic acid (17.17 mL), sodiumacetate/trihydrate (27.21 gm), calcium chloride dihydrate (0.118 gm) andsufficient distilled water to make up a 4.0 L solution. With gentlemixing powdered corn starch is added (1.0 kg) followed by AMG300L enzymesolution (40.0 mL) (NovoNordisk). Stirring is continued for 30 hours at23° C. The resulting solution is filtered through a double thickness ofWhatman No. 4 paper and the solid product is washed with about 2 L ofwater then with about 500 mL of ethanol. The product is air dried andyields 724 gm. The modified starch is then oven dried for about 5 hoursin an oven set at 110° C. to yield 648 gm of an odorless, white,free-flowing powder. The product is used for coating with siloxaneswithout further need for purification.

EXAMPLE 2

Dissolve ABIL AV-1000 siloxane (Goldschmidt) (15 gm) in toluene (150mL). Porous corn starch (20% void volume, ˜0.20 cc/gm, preparedaccording to U.S. Pat. No. 4,985,082) is pre-dried at 110° C. for 4hours. A sample of the starch (30 gm) is added to the solution of ABILand heated to a boil for about 2 minutes then cooled to roomtemperature. The slurry is isolated by filtration, dried in air, thendried at 100° C. for 19 hours to yield a free flowing solid suitable fordirect use in a catamenial, diaper or in conjunction with other malodorproducing materials.

EXAMPLE 3

Dissolve ABIL AV-1000 siloxane (Goldschmidt) (15 gm) in isopentane (150mL). Porous corn starch (20% void volume, ˜0.20 cc/gm, preparedaccording to U.S. Pat. No. 4,985,082) is pre-dried at 110° C. for 4hours. A sample of the starch (30 gm) is added to the solution of ABILand heated to a boil for about 2 minutes then cooled to roomtemperature. The slurry is isolated by filtration, dried in air, thendried at 100° C. for 19 hours to yield a free flowing solid suitable fordirect use in a catamenial, diaper or in conjunction with other malodorproducing materials.

U.S. Pat. No. 5,308,346, Sneller et al., issued May 3 1994, discloses aunitary disposable absorbent article having an elasticized side flap byoperatively associating an elastic member on both the upper surface andlower surface of the side flap. These articles may be used as acatamenial or an incontinence article. The modified starch granulesprepared according to Examples 2 or 3 are added to the absorbentsubstrate that comprises the unitary disposable absorbent article in anamount at least 10% by weight of the absorbent material. The resultingmodified disposable absorbent article is suitable for use by a wearerwherein diminished malodor is desirable.

What is claimed is:
 1. A material for absorbing a hydrophobic compoundcomprising:a) a partially hydrolyzed porous starch matrix, the starchhaving a surface; and b) a siloxane surface modifying agent applied tothe porous starch matrix, wherein the modifying agent renders thesurface of the starch substantially hydrophobic.
 2. The absorbentmaterial according to claim 1 wherein the porous starch matrix comprisesstarch granules partially hydrolyzed with an amylase enzyme.
 3. Theabsorbent material according to claim 2 wherein the porous starch iscorn starch, potato starch, or mixtures thereof.
 4. The absorbentmaterial according to claim 3 wherein the porous starch is corn starch.5. The absorbent material according to claim 4 wherein the siloxanesurface modifying agent has the formula ##STR3## wherein R¹ units are C₂-C₂₂ linear alkyl, C₃ -C₂₂ linear alkenyl, C₂ -C₂₂ branched alkyl, C₃-C₂₂ branched alkenyl, phenyl, benzyl, phenoxy, benzyloxy; R² units are--(OR³)_(n) R⁴ or --(CH₂)_(m) (OR³)_(n) R⁴ wherein R³ is C₂ -C₁₂alkylene; R⁴ is hydrogen, C₁ -C₁₂ alkyl, or NR⁵ R⁶, wherein R⁵ and R⁶are each independently C₂ -C₂₂ linear alkyl, C₃ -C₂₂ linear alkenyl, C₂-C₂₂ branched alkyl, C₃ -C₂₂ branched alkenyl, phenyl, benzyl, phenoxy,benzyloxy, and mixtures thereof; the value of m is from 1 to 22; thevalue of n is from 1 to 22; the value of x is from 0 to about 10,000;the value of y is from about 0 to about 10,000; the value of z is from 0to about 10,000.
 6. The absorbent material according to claim 5 whereinR⁴ units are selected from the group consisting of hydrogen, methyl, andmixtures thereof.
 7. A method for absorbing a hydrophobic compound froman aqueous-based medium comprising the step of contacting theaqueous-based medium with a surface modified microporous starch granulecomprising a partially hydrolyzed porous starch matrix and a siloxanesurface modifying agent applied to the porous starch matrix, wherein themodifying agent renders the surface of the starch granule substantiallyhydrophobic.
 8. The method according to claim 7 wherein the porousstarch matrix is corn starch.
 9. A method for absorbing a hydrophobicmaterial comprising the step of contacting the hydrophobic materialhaving a ClogP greater than 1 with an absorbent material comprising apartially hydrolyzed porous starch matrix and a siloxane surfacemodifying agent applied to the porous starch matrix, wherein themodifying agent renders the porous starch matrix substantiallyhydrophobic.